The following discussion is provided solely to assist the understanding of the reader, and does not constitute an admission that any of the information discussed or references cited constitute prior art to the present invention.
Throughout the world, cow's milk has become a nearly universal part of the human diet, particularly for growing children and young adults. Milk provides high quality protein in the form of casein and whey, as well as minerals such as calcium, carbohydrate in the form of lactose, vitamins, and varying amounts of fat depending upon whether a consumer purchases full fat milk containing 4% milkfat, or alternatively reduced fat milk containing either 2% or 1% milkfat. For individuals who need to limit their intake of fat and cholesterol, fat free or skim milk is available, containing, only a trace amount of milkfat (also known as butterfat). Milk is used to produce a variety of other food products including creams, a wide variety of cheeses including cottage cheese, as well as cultured yogurt, buttermilk, sour cream, ice cream, and many other dairy products.
Milk Chemistry
Milk is an emulsion of butterfat globules within a water-based fluid. Each fat globule is surrounded by a membrane-like layer containing phospholipids and proteins. These membrane components keep the individual fat globules from joining together into larger particles of butterfat and also protect the globules from lipase enzymes found in the fluid portion of the milk. In non-homogenized cow's milk, the diameter of fat globules averages about four microns. The fat-soluble vitamins, A, D, E and K are found within the milkfat portion of the milk.
The most prevalent structures in the fluid portion of the milk are casein protein micellar aggregates whose structure also involves very small particles of calcium phosphate. Each micelle is roughly spherical and is about a tenth of a micrometer in diameter. There are four different types of casein proteins, and collectively they constitute approximately 80 percent of the protein in milk, by weight. Most of the casein is bound in micelles. It is generally agreed that outermost layer consists of strands of one type of protein, kappa-casein, extending out from the body of the micelle into the surrounding fluid. These molecules have a negative electrical charge and repel each other, keeping the micelles separated under normal conditions and in a stable colloidal suspension.
Both the fat globules and the smaller casein micelles, which are just large enough to deflect light, contribute to the opaque white color of milk. The native fat globules generally contain some yellow-orange carotene that may impart a creamy hue to a glass of milk. Fat-free skim milk on the other hand, contains only the smaller casein micelles to scatter light, and they tend to scatter shorter-wavelength blue light more than red, giving skim milk a bluish tint.
Milk contains dozens of other types of proteins besides the caseins. They are more water-soluble than the caseins and do not form actual structures in the milk like the caseins. Because these proteins remain dispersed in the whey if casein proteins are induced to coagulate into curds, they are collectively known as whey proteins. Whey proteins including lactoglobulin make up around twenty percent of the protein in milk, by weight.
Upon standing for 12 to 24 hours, fresh milk has a tendency to separate into a high-fat cream layer on top of a larger, low-fat milk layer. The separation of the cream from the milk is usually accomplished rapidly in centrifugal cream separators. With non-homogenized milk, the fat globules rise to the top of a container of milk because fat is less dense than water. The larger the fat globules, the faster the cream separates.
With regard to homogenization, milk is homogenized to prevent the cream layer from separating out of the milk. The milk is typically pumped at high pressures through very narrow tubes, breaking up the fat globules through turbulence and high shear. As the fat globules are broken into many smaller particles that possess more total surface area, the original fat globule membranes cannot re-form. The abundant small casein micelles are attracted to the newly-exposed surfaces of these smaller fat particles. Association with the casein micelles increases the density of the smaller fat globules and interferes with their clustering that would otherwise accelerate cream separation. Immediate pasteurization inactivates endogenous lipase enzymes that would otherwise attack the newly exposed surfaces of the smaller fat globules produced during homogenization. It is interesting to note that unlike pasteurization, homogenization confers no health or safety benefits to the milk, only the convenience of not needing to shake the bottle to distribute milkfat.
Omega-3 Fatty Acids.
Omega-3 fatty acids constitute a family of polyunsaturated fatty acids that are recognized as providing a wide range of health benefits when consumed as a regular part of the human diet. The most well known omega-3 fatty acids include alpha-linolenic acid (ALA) that is found in soybean oil, canola oil and flaxseed oil, as well as docosahexaenoic acid (DHA), and eicosapentaenoic (EPA) commonly found in fish oil and other marine oils. All of these fatty acids contain multiple carbon-carbon double bonds including one double bond in the omega-3 or third position inward from the distal end of the fatty acid chain that is attached at its opposite end by an ester linkage to the glycerol backbone of the triglyceride molecule.
While the human body is not capable of synthesizing omega-3 fatty acids from other nutrients, it is able to convert some of the dietary alpha-linolenic acid that is 18 carbons in length, to the longer 20 and 22 carbon chain EPA (20:5 n-3) and DHA (22:6 n-3) molecules. Both the omega-3 fatty acids and the omega-6 fatty acid, linoleic acid (18:2n-6), are termed “essential nutrients” because they are largely obtained from foods rather than synthesized by the body.
In recent years, the U.S. FDA allowed a “qualified health claim” to be made with regard to the dietary consumption of EPA and DHA, stating that “supportive but not conclusive research shows that consumption of EPA and DHA omega-3 fatty acids may reduce the risk of coronary heart disease.”
A variety of medical conditions have been reported to be ameliorated by regular dietary consumption of EPA and DHA. Some of these conditions include improvement in blood circulation, control of heart arrhythmias, beneficial control of clot formation, reduction in blood pressure, beneficial reduction of blood triglyceride levels, reduced risk of primary and secondary heart attacks, and improvements covering wide range of inflammatory diseases including rheumatoid arthritis. Some research has suggested that fish oil may limit the risk of thrombotic and ischemic stroke as well, while beneficially reducing the amount of LDL cholesterol oxidation that occurs in the bloodstream and that may contribute to atherogenesis.
Some studies indicate that the incidence of certain forms of cancer including prostate, breast and colon is reduced by substantial dietary intake of omega-3 fatty acids. Still other research has suggested that omega-3 fatty acids may ameliorate conditions of psychological depression and anxiety.
While maximum safe levels of EPA and DHA have not been established, it is believed that daily intake of 4 grams EPA and 2 grams DHA are not excessive. Since many typical fish oils contain approximately 30% by weight EPA+DHA, it is likely that consuming up to 20 grams per day of fish oil would result in no adverse health effects. Many people consume between one and six 1 g capsules of fish oil per day, providing between approximately 300-1800 mg of EPA and DHA. While these levels may be desirable goals for many health-conscious individuals, it is believed that making even a fraction of these levels available to the general public by supplementing conventional foods will result in a significant public health benefit.